Final answer:
The correct option is 1. Synapomorphies among species indicate that they share a common ancestor, which assists scientists in constructing phylogenetic trees and understanding evolutionary history.
Step-by-step explanation:
Synapomorphies among a group of species provide evidence that the species share a common ancestor. This concept is essential in the study of evolutionary biology, particularly when constructing phylogenetic trees and cladograms. A synapomorphy is a trait that originated in an ancestor and is present in its descendants, allowing scientists to infer evolutionary relationships.
In the context of phylogenetics, when scientists observe certain traits that are shared across different organisms, they must determine whether these traits are homologous or analogous. Homologous traits are those that are inherited from a common ancestor, while analogous traits arise from convergent evolution. Using various methods, including DNA sequencing, scientists can differentiate between these traits to establish a more accurate evolutionary history.
To determine the evolutionary path and relationships among species, scientists depend on the principles of cladistics, which include the assumptions that species evolve from a common ancestor and traits change over time, determining new branch points in the tree of life. When constructing a phylogenetic tree, shared derived characters, such as the amniotic egg in some vertebrates, are essential in distinguishing different groups and determining the relatedness of species.
Therefore, the shared derived traits or synapomorphies provide compelling evidence of a common ancestor rather than traits evolving independently (convergence) or originally evolving for a different function (exaptations). The correct option, in this case, would be the first one: the species share a common ancestor.